In many electronic systems, the efficient cooling of electronic components has become a significant problem. With the advent of large-scale integrated circuit (IC) modules containing many thousands of circuit elements, it has become possible to pack great numbers of electronic components together within a very small volume. As is well known, these integrated circuit modules generate significant amounts of heat during the course of their normal operation. Since most solid state devices are sensitive to excessive temperatures, a solution to the problem of the generation of heat by large scale IC's in close proximity to one another has become of increasing concern to industry.
A typical prior art approach to cooling electronic components is to direct a stream of cooling air across the modules and/or circuit cards carrying such devices. However, the increasing power density of electronic systems is reaching the point where it is no longer possible to adequately cool heat generating electronic components by forcing air over them. Power densities are anticipated to reach the point where it is physically impossible to force sufficient ambient temperature air through a cabinet to adequately cool the electronics inside. Several other disadvantages to this approach have also been identified, including: high pressure drop; uniformity of component form factors; placing the components containing the integrated circuits further apart on the circuit cards; increasing the distance between circuit cards; and increasing the volume and velocity of cooling air directed over the components. This required increase in volume and velocity of cooling air requires special considerations in the design of the housings containing the circuit cards and in the mechanical systems for delivering the cooling air. Also, the air quality (moisture content, contamination, etc.) must be tightly controlled to inhibit corrosion, loss of cooling effectiveness, etc. Thus, cooling of components by this means necessitates a number of compromises to the overall system that prevent its use in many systems.
The foregoing thermal management problems have brought about the evolution of other techniques for cooling card-mounted electronic components. For example, one technique includes the use of solid metal thermal mounting cards or plates which conduct the heat dissipated by electronic components to a heat sink (cold plate) disposed at the edge of each circuit card. Such an approach, however, results in a large thermal resistance from the component mounting surface to the heat sink, which causes high component temperatures.
Other known techniques for cooling electronic systems include loop thermosyphons and heat pipes. Loop thermosyphons are devices that use gravity to maintain two-phase fluid circulation during operation. Each loop thermosyphon has an evaporator, where vaporization occurs when it is heated, a vapor conduit through which the vapor flows to a condenser where it is cooled and condenses, and a liquid return conduit to return the liquid to the evaporator. Sometimes a capillary structure is used in the evaporator to reduce its thermal resistance.
A problem is often associated with prior art loop thermosyphons in that leakage occurs at the liquid return line interface with the condenser. This ocurance often results in the need for hermetic sealing at that interface that greatly increases the cost of the device, and often limits the flexibility of the conduits.